fix failing doctests

Author: simon-king-jena

src/sage/algebras/letterplace/free_algebra_letterplace.pyx

@@ -252,8 +252,6 @@ cdef class FreeAlgebra_letterplace(Algebra):
             varnames = R.variable_names()[:-1]
             self._nb_slackvars = 1
         base_ring = R.base_ring()
-        Algebra.__init__(self, base_ring, varnames,
-                         normalize=False, category=Algebras(base_ring))
         self._commutative_ring = R
         self._current_ring = make_letterplace_ring(R,1)
         self._degbound = 1
@@ -264,8 +262,8 @@ cdef class FreeAlgebra_letterplace(Algebra):
                 raise TypeError("The generator degrees must be given by a list or tuple of %d positive integers" % (self.__ngens-1))
             self._degrees = tuple([int(i) for i in degrees])
             self.set_degbound(max(self._degrees))
-        self._populate_coercion_lists_(coerce_list=[base_ring])
-
+        Algebra.__init__(self, base_ring, varnames,
+                         normalize=False, category=Algebras(base_ring))
     def __reduce__(self):
         """
         TESTS::

src/sage/categories/pushout.py

@@ -3660,10 +3660,14 @@ def pushout(R, S):
         [1 2 0]
         [0 0 1]
 
-    Some more tests with ``coercion_reversed = True``::
+    Here are some more tests with ``coercion_reversed = True``. Note that
+    in the following test, we are not inheriting from ``type(QQ['x'])``,
+    since this already inherits from a category's parent class: If this
+    is the case for a class, the the category framework will not be correctly
+    initialised for instances of this class. ::
 
         sage: from sage.categories.pushout import ConstructionFunctor
-        sage: class EvenPolynomialRing(type(QQ['x'])):
+        sage: class EvenPolynomialRing(type(QQ['x']).__base__):
         ....:     def __init__(self, base, var):
         ....:         super(EvenPolynomialRing, self).__init__(base, var)
         ....:         self.register_embedding(base[var])

src/sage/structure/parent.pyx

@@ -344,12 +344,12 @@ cdef class Parent(sage.structure.category_object.CategoryObject):
             # this calls __init_extra__ if it is *defined* in cls (not in a super class)
             if "__init_extra__" in cls.__dict__:
                 cls.__init_extra__(self)
-        if not ((category is None) or isinstance(self, category.parent_class)):
+        if category is not None:
             # This is the case if and only if self is an instance of an
             # extension class. Now, we should go up the class hierarchy
             # of the category's parent class and seek for "__init_extra__".
             for cls in category.parent_class.mro():
-                if "__init_extra__" in cls.__dict__:
+                if not isinstance(self, cls) and "__init_extra__" in cls.__dict__:
                     getattr_from_other_class(self, cls, '__init_extra__')()
 
     def _init_category_(self, category):